diff options
Diffstat (limited to 'src/devices/audio_avoiding_pi.jd')
| -rw-r--r-- | src/devices/audio_avoiding_pi.jd | 39 |
1 files changed, 18 insertions, 21 deletions
diff --git a/src/devices/audio_avoiding_pi.jd b/src/devices/audio_avoiding_pi.jd index a8cd208c..49b901e8 100644 --- a/src/devices/audio_avoiding_pi.jd +++ b/src/devices/audio_avoiding_pi.jd @@ -42,14 +42,14 @@ allows the audio buffer sizes and counts to be reduced while still avoiding artifacts due to underruns. </p> -<h2 id="priorityInversion">Priority Inversion</h2> +<h2 id="priorityInversion">Priority inversion</h2> <p> <a href="http://en.wikipedia.org/wiki/Priority_inversion">Priority inversion</a> is a classic failure mode of real-time systems, where a higher-priority task is blocked for an unbounded time waiting -for a lower-priority task to release a resource such as [shared -state protected by] a +for a lower-priority task to release a resource such as (shared +state protected by) a <a href="http://en.wikipedia.org/wiki/Mutual_exclusion">mutex</a>. </p> @@ -64,7 +64,7 @@ are used, or delay in responding to a command. <p> In the Android audio implementation, priority inversion is most -likely to occur in these places. And so we focus attention here: +likely to occur in these places. And so you should focus your attention here: </p> <ul> @@ -99,10 +99,10 @@ not yet implemented. The likely priority inversion spots will be similar to those for AudioTrack. </p> -<h2 id="commonSolutions">Common Solutions</h2> +<h2 id="commonSolutions">Common solutions</h2> <p> -The typical solutions listed in the Wikipedia article include: +The typical solutions include: </p> <ul> @@ -130,18 +130,17 @@ Priority inheritance in Linux kernel, but are not currently exposed by the Android C runtime library <a href="http://en.wikipedia.org/wiki/Bionic_(software)">Bionic</a>. -We chose not to use them in the audio system -because they are relatively heavyweight, and because they rely on -a trusted client. +They are not used in the audio system because they are relatively heavyweight, +and because they rely on a trusted client. </p> <h2 id="androidTechniques">Techniques used by Android</h2> <p> -We started with "try lock" and lock with timeout. These are +Experiments started with "try lock" and lock with timeout. These are non-blocking and bounded blocking variants of the mutex lock -operation. Try lock and lock with timeout worked fairly well for -us, but were susceptible to a couple of obscure failure modes: the +operation. Try lock and lock with timeout worked fairly well but were +susceptible to a couple of obscure failure modes: the server was not guaranteed to be able to access the shared state if the client happened to be busy, and the cumulative timeout could be too long if there was a long sequence of unrelated locks that @@ -167,10 +166,9 @@ SMP barriers. The disadvantage is they can require unbounded retries. In practice, we've found that the retries are not a problem. </p> -<p> -<strong>Note</strong>: Atomic operations and their interactions with memory barriers -are notoriously badly misunderstood and used incorrectly. We include -these methods here for completeness but recommend you also read the article +<p class="note"><strong>Note:</strong> Atomic operations and their interactions with memory barriers +are notoriously badly misunderstood and used incorrectly. These methods are +included here for completeness but recommend you also read the article <a href="https://developer.android.com/training/articles/smp.html"> SMP Primer for Android</a> for further information. @@ -234,7 +232,7 @@ such as PCM audio where a corruption is inconsequential. </ul> -<h2 id="nonBlockingAlgorithms">Non-Blocking Algorithms</h2> +<h2 id="nonBlockingAlgorithms">Non-blocking algorithms</h2> <p> <a href="http://en.wikipedia.org/wiki/Non-blocking_algorithm">Non-blocking algorithms</a> @@ -273,9 +271,8 @@ suitable for other purposes. </p> <p> -For developers, we may update some of the sample OpenSL ES application -code to use non-blocking algorithms or reference a non-Android open source -library. +For developers, some of the sample OpenSL ES application code may be updated to +use non-blocking algorithms or reference a non-Android open source library. </p> <h2 id="tools">Tools</h2> @@ -297,7 +294,7 @@ are useful for seeing priority inversion after it occurs, but do not tell you in advance. </p> -<h2 id="aFinalWord">A Final Word</h2> +<h2 id="aFinalWord">A final word</h2> <p> After all of this discussion, don't be afraid of mutexes. Mutexes |